Nuclear Magnetic Relaxation Times and the Microdynamic Structure of Liquid Mixtures.

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glucosamine ( [ K ] I=~ +32.3 ’) and the N-glycolylneuraminic
acid ([cr]’f
= -33.5 ”) can be obtained in crystalline from.
c H ,OH
II-C-OH
Hcl/ntirrli Fisclicv, Karlsruhe (Germany)
11-C -OH
OH
H
The intrinsic factor, a glycoprotein of human gastric mucosa,
contains N-acetylneurarninic acid, which protects the biologically active protein portion of this molecule from attack by
trypsin in the digestive tract (research in collaboration with
W. Pribilla). If N-acetylneuraminic acid is eliminated with
neuraminidase, the intrinsic factor is attacked by trypsin and
loses its power t o promote the resorption of vitamin BIZ in
the intestine. Protection against trypsin is also obtained if
N-acetylneuraminic acid in the intrinsic factor is replaced by
the cation exchanger poly(acry1ic acid vinyl pyrrolidone).
[GDCh-Ortsverband Miilheim/Ruhr (Germany),
January 6th, 19651
[VB 9041209 IE]
German version: Angew. Chem 77, 432 (1965)
Nuclear Magnetic Relaxation Times and the
Microdynamic StGcture of Liquid Mixtures
H . G. Hertz, Miinster (Germany)
There is relatively little knowledge, mostly from spectroscopic
investigations, about the preferred spatial arrangement of
molecules in liquid mixtures, i . e . about the “structure” of
mixtures. The “microdynamic structure” of a liquid is
characterized by dividing the liquid into microscopic regions
and ascribing to each of these regions a molecular reorientation and residence time. Thus it is possible, for example, to
correlate changes in the thermodynamic excess functions on
variation of the composition of the mixture with changes in
the microdynamic structure. The molecular reorientation
and residence times may be obtained by measuring the
nuclear magnetic relaxation times or the decay of the spinecho amplitude (self-diffusion coefficient).
This method was applied to the study of the hydration of
large, singly charged ions, e . g . Br-, I-, Rb+ [l]. By combining results of measurements of relaxation times for protons
with those for the large ions, it was shown that the range of
the increased fluidity, as compared with pure water, extends
right to the surface of the ion. I n other words, the hydration
sphere around the ions is not rigid. The activation energy
for reorientation of the water molecules in the hydration
sphere lies between 2 and 3 kcal/mole, i.e. below that for
pure water. Measurements of relaxation times also show
that the time for reorientation of the water molecules in the
hydration sphere around non-polar groups ( e . g . alkyl groups)
is about twice as high as in pure water 121. This effect has
been described as “iceberg formation”[3) or “hydration of the
second kind” [4]. The reorientation times of the dissolved
particles and the activation energy for this process can be
determined by isotopic substitution and extrapolation to
infinite dilution. Smaller particles containing alkyl groups
have a high mobility within their hydrate cages. These
relationships were studied for the systems acetonelwater and
methanol/water over the entire composition range.
[GDCh-Ortsverband Gottingen (Germany),
[VB 905/21! IE]
January 14th, 19651
German version: Angew. Chem. 77, 453 (1965)
. .
....
[ I ] H . G . Hertz, Ber. Bunsenges. physik. Chern. 67, 3 1 1 (1963);
H . G. Hertz and M. D.Zeidler, ibid. 67, 174 (1963).
[2] H. G . Hertz and M . D. Zeidler, Ber. Bunsengcs. physik.
Chem. 68, 821 (1964).
[3] ff. S. Frank and M . W. Evans, J . chem. Physics 13,507 (1945).
[4] ff. G. Hertz, Ber. Bunsenges. physik. Chem. 68, 907 (1964).
446
Control of Electrochemical Reactions by Means of
Foreign Sorbates
The sorption of foreign substances and their orientation on
a metallic surface largely depend on the surface charge of
the metal, which may be varied by means of a potential. This
constitutes the principal difference in the efficiency of such
sorbates in electrochemical and in non-electrochemical heterogeneous reactions. The following examples were given for
the effect, dependent on potential, of a sorbed foreign substance in electrode reactions:
1. During the dissolution of iron in acid, the anodic transfer
of iron into the solution, which is accelerated by sorbed hydroxide ions, may be inhibited by more strongly surface-active sorbates, e . g . chloride, other anions or polar molecules
such as phenylthiourea, as a function of the potential.
2. The drastic effect of a potential-controlled change from
adsorption to desorption (or vice versa) is shown, e.g. in the
evolution of H2 or in the deposition of Ni on a nickel
cathode (marked change in capacity, coverage of deposit,
and overvoltage).
3. A galvanostatic formation of rhythmic-lamellar structures,
coupled with periodic potential fluctuations, can be observed
when copper is deposited in the presence of o-phenanthroline. The overvoltage alters with the abrupt changes in the
sorptive coating, and in each period nucleation, specific crystal
growth, and levelling of the deposit occur in turn.
4. In the case of electro-crystallization, the sorbates may be
incorporated into the metal. Electron microscopy and spectrophotometry indicate occlusion densities of the same order,
e. g . 1018- 1020 molecules/cmz for o-phenanthroline in Ni.
5. The inhibition by sorbed 5,6-benzoquinoline, which varies
over a wide potential range (about 800 mV), was discussed
using the redox system V3”/VZc/Hg as an example. By
comparing the current density vs. potential curves in 0.1 N
HCl and in 0.1 N HCI + 0.9 N KCI, mechanical blocking of
the surface may be distinguished from a n electrokinetic effect
(repulsion between V3+ and VZ+). Potential vs. capacity curves, taken in vanadium-free electrolytes under otherwise
similar conditions, confirm the occurrence of inhibition and
sorption of foreign substances within the same potential
ranges.
IGDCh-Ortsverband Freiburg (Germany),
January 15th, 19651
[VB 906/213 IE]
German version: Angew. Chem. 77, 459 (1965)
Recent Investigations of Covalent
Inorganic Fluorides
0. Glemser, Gottingen (Germany)
Difluorodiazine N2Fz is obtained by direct fluorination of
NaN3 in a continuous process at room temperature. On
adding chlorine to the fluorine, highly explosive chlorofluorodiazine N2FCI is produced. On passing NO with
fluorine at 65OoC through a CaFz tube, nitrogen trifluoride
is formed:
2 N O + 2F2
+- N O p F f N F 3
NF3 is often considered to be only slightly reactive. On being
passed into molten sulfur at 200 OC it yields a little N3S3F3,
but at 400 OC good yields of thiazyl fluoride NSF and thiothionyl fluoride SSF2 are obtained. In this way NSF and
SSFz can be obtained easily on a preparative scale.
Nitrogen-sulfur-fluorine compounds can be divided into the
acyclic compounds NSF, S3NzF2, NSF3, and the cyclic
compounds N4S4F4, N3S3F3, S4N3F. Of the former, NSF3
can be reacted with diethylamine to give the stable compound
NSFzN(CzH& which contains an N E S triple bond as does
NSF3.
Angew. Chem. interntit. Edit. / Vol. 4(1965)
/
No. 5